This invention relates to the control of a motor vehicle air conditioning system, and more particularly to a control that reduces head pressure spikes caused by high compressor acceleration.
In a motor vehicle air conditioning system, the refrigerant compressor is customarily driven by the vehicle engine through a mechanical advantage drive such as a belt and pulley system. As a result, engine speed transients produce similar or more severe transients in the air conditioning system. A particularly severe transient occurs during acceleration of the vehicle from standstill, as the compressor speed can rise several thousand revolutions per minute in a matter of seconds. In this case, the transient is manifested by a sharp rise, or spike, in the compressor outlet pressure, which if unchecked, can damage or otherwise degrade the operation of various components, including the compressor itself.
In a conventional system, the high side pressure spike concern is addressed by measuring the high side pressure (with a pressure switch, for example), and de-coupling the compressor from the engine when the measured pressure exceeds a predefined threshold. However, de-coupling the compressor in this manner significantly degrades air conditioning performance and raises durability issues in respect to components such as the compressor clutch. Accordingly, what is needed is an improved way of addressing the transient pressure concern that does not significantly compromise passenger comfort or degrade the system durability.
The present invention is directed to an improved system and method for suppressing high side pressure transients in a motor vehicle air conditioning system due to engine speed transients during vehicle acceleration through the use of a throttling valve. The throttling valve may be mechanically or electrically activated, and is connected in the low pressure side of the air conditioning system to controllably restrict refrigerant flow in response to one or more parameters that detect or anticipate a high side transient pressure condition. The parameters may include the high side pressure itself, or engine parameters such as engine speed and vehicle speed. In a preferred embodiment, the throttling valve may be controlled to prevent evaporator icing in addition to suppressing high side pressure transients.